This invention relates to a device for changing the downward stroke of a rivet head forming tool of a rivet head caulking machine.
In a prior art caulking machine, a rotary shaft is moved up and down within a predetermined stroke by actuating a cylinder to bring a forming shaft of a rivet head forming tool mounted on the bottom end of the rotary shaft into abutment with the end of a rivet shank at the end of the stroke. Thus a rivet head is formed.
Also, the up and down stroke of an anvil is adjustable according to the length of the rivet shank.
But if a plurality of rivet shanks having different lengths are provided on an article, it is necessary to repeat the operation of caulking a group of rivet shanks having equal lengths to one another and changing the anvil position to caulk another group of rivet shanks having equal lengths to one another. Otherwise it is necessary to use a plurality of caulking machines each for caulking a group of rivet shanks having equal lengths to one another. This is troublesome and extremely inefficient.
Japanese Unexamined Utility Model Publication 62-159940 shows a solution to this problem in which an article provided with rivet shanks of different lengths (protruding from the end faces of pins and extending through a plate) is placed on a table.
Then, the table is moved back and forth and side to side based on data inputted according to the positions of the first to last rivet shanks so that the rivet shanks will be brought right under the rivet head forming tool one after another.
On the other hand, an annular plate is driven by a drive unit. When a detector detects that pins having a length corresponding to that of the rivet shank to be caulked, i.e. adapted to restrict the downward stroke of the rivet head forming tool is located right under stopper pins, the annular plate is stopped.
When the rivet head forming tool is lowered together with the rotary shaft by a cylinder, the bottom ends of the stopper pins will abut the top ends of the pins, thus restricting the downward stroke of the rivet head forming tool. Thus, a forming surface of the forming shaft of the rivet head forming tool abuts the end of the rivet shank to form a rivet head.
When the detector detects that the pins for restricting the downward stroke of the rivet head forming tool are located right under the stopper pins while the annular plate is being driven by the drive unit (motor), the drive unit is deactivated to stop the annular plate. Thus, it was impossible to stop the stopper pins and the down stroke restrictor pins so that they will align with each other due to the inertia of the motor after it has been stopped.
Therefore, it was impossible to restrict the down stroke of the rivet head forming tool. This may result in the breakage of articles and rivet shanks.